Automatic adjustment foe



June 3, 1941. E. TRACHSEL AUTOMATIC ADJUSTMENT FOR BRAKES Original FiledFeb. 23, 1958 I5 Sheets-Sheet 2 r m 6 V ur M u H 5 a 9 a u 7% T 7 3 5 wJune 3, 1941. E. TRACHSEL AUTOMATIC ADJUSTMENT FOR BRAKES OriginalFiledFeb. 25, 1938 3 Sheets-Sheet 3 Reissued June 3, 1941 AUTOMATICADJUSTMENT FOR BRAKES Ernst Trachsel, Zurich, Switzerland, assignor ofsixty per cent to Walther Huessy, Aarburg,

Switzerland riginal No. 2,183,416, dated December 12, 1939,

Serial No. 1312,053, February 23, 1938.

'Application for reissue August 31, 1940, Serial No.

21 Claims.

The present invention relates to braking apparatus of the internalexpanding type as em,- ployed in motor vehicles and more specifically toa means for effecting automatically the adjustment of brake blocks tocompensate for wear of the linings of the same, so that the length ofpath of such brake blocks to cause their contact with the inner face ofthe usual brake drum for shaking is rendered constant.

Many proposals have been made of mecha nisms which, on the path of thebrake blocks being exceeded on the braking stroke due to wear of brakelinings, would cause a brake block to move back on brake release alittle less distance than the length of its last forward or brakingstroke. Whilst the consequent braking strokes have therefore the correctlength of path, that path is itself moved forward towards the brake drumto leave the normal clearance space between drum and brake lining whenthe brakes are off. It is essential however to remember that a brakedrum will on occasion expand due to heat generated in braking, and thisexpansion may extend to several millimetres increase of drum diameter,so that in these circumstances,

the brake blocks will adjust themselves in accordance with an increasedlength of braking path which is only temporarily established and isnullified when the brake drum shrinks again on cooling, the said brakeblocks are liable to become jammed or the necessary clearance spacebetween brake drum and brake lining will be rendered too narrow by suchadjustment.

The objects of the present invention are, firstly, to provide a meansfor automatic brake adjustment which will allow for the conditions justset forth; secondly, to provide in combination with this a means forautomatic adjustment of each of a pair of brake blocks separately in theone braking mechanism; and thirdly, to provide a mechanism for thesepurposes which will be recluced to the minimum as to number of parts andhave the maximum of surety of operation and durability.

With these desirable objects in view the invention consists in theemployment, in conjunction with a brake block, of a feeler member whichis movable towards the brake drum, on braking movement of a brake block,to make contact with such drum, the length of the path of movement offeeler member being equivalent to the normal length of braking movementpath of the brake block. Adjusting means for provided between the brakeblock and the feeler member, this adjustment being so arranged that whenthrough In Switzerland March '2, 1937 wear or other causes a brake blocklining face does not in braking make contact with the brake drum at thesame instant that the feeler member contacts with such drum, the excessof movement of the lining causes the adjustment means to adjustthemselves and increase the efiective distance between the feeler memberand the brake block to Which it is connected; the

path of movement of the brake block is thus pro tanto moved towards thebrake drum. Where a hard and prolonged braking has caused expansion ofthe brake drum, the point at which the adjusting means come into actionwill be delayed, as will be understood. For example, if a. brake blockis in perfect order with anew and unworn lining, both the face of thelining and the face of the feeler' member will touch the ex! panded drumtogether and there is therefore nofalse adjustment of the path of thebrake block.

This provision is. in itself highly desirable and in fact essential, butit is also essential that any adjusting means for the purpose statedshall be of such a nature that there will be no chattering or danger ofuneven working, The use of small and. weak parts is also to be avoided,and to avoid these undesirable conditions I mount the means forconnecting the adjusting member and the feeler member very strongly uponthe backplate of the brake assembly, The anchorage pins of a pair ofbrake blocks may in fact be utilised to receive these connecting means,thus ensuring great strength, durability and firmness, resulting uponthe mounting of the said means upon the backplate, and the saving of theprovision of extra. means for the purpose.

The invention may be applied indifferently to that form of internalexpanding brake in which the brake shoes are anchored upon adjacentanchorage pinsupon the backplate, both brake blocks being applied tothebrake drum by means such as a hydraulic cylinder with pistons, whichexpand both brakes; and to a further form in which the brake blocks arepivotally anchored at opposed sides of the backplate, each beingactuated by such means as a separate hydraulic cylinder and piston.Application of the invention to these two forms is shown in the annexeddrawings, in which:

Figure 1 is an elevation of a brake assembly of the first mentionedtype, Figure 2 being a cross section taken on line I- II of Figure 1;

Figure 1a is a detail in longitudinal section showing a form ofadjusting means provided between a brake block and a feeler member;

Figure 3 is a fragmentary showing of the same form of brake in which theanchorage pins of the brake blocks are employed as bearings for theadjustment means;

Figure 4 is an elevation of the second above named type of brake withthe adjustment means applied using the anchorage pins of the brakeblocks.

Figure 5 is an elevation of a brake of the typ shown in Figure 4 buthaving a modified form of adjusting means; and

Figures 6 and 7 are cross-sections taken on lines VI-VI and VII--VIIrespectively of Figure 5.

Referring first to Figures 1, 1a and 2, a usual backplate is shown at 3and it bears pivot pins 4 on which pivot the two brake shoes 5 havingthe linings 6, each shoe and its lining constituting a brake block. Asin known practice in-hydraulic brakes a double piston 1 serves tocomwhich, as usual with brake block linings, may be riveted in place.This constitutes the feeler member, and near its upper extremity it isperipherally recessed at M to receive pins I5--'one of which isshown-each of which is fixed in the end of an arm of a pivoted bellcranklever I 6,

the extremity of the other arm of which bellcrank lever is articulatedto a tubular member I1 in which fits a rod H! which is at its outerextremely articulated to 'a brake shoe 5 at IS; The tubular members I!are internally threaded and longitudinally slit as shown at 20, and anexternal thread 2| on each rod l8 engages the internal thread of itsmember ll. A pull upon a rod 18 therefore, the tubular member l1resisting, will cause the rod and tubular member, considered as a whole,to extend and be retained -in that condition, the said tubular memberbeing laterally yieldable on such pull.

In operation the brake-blocks are normally at a given distance from thebrake drum 8 when the brakes are off. The feeler member face I 3 is atsubstantially the same distance from the drum. On the brakes beingapplied, the feeler member facing l3 touches the drum, and the brakelinings 6 make contact therewith, simultaneously, due allowance beingmade for any compressibility of the said linings under braking pressure.In course of time wear of a brake lining takes place,, and this causesit to continue in its braking path'a'fter the feeler member facing hasmade contact with and been arrested by the brake drum. There istherefore a resistance to further movement of the tubular member I! ofthe block, and. the rod [8 is drawn out to an extent equal to the excessmovement of such brake block. That is to say, when a lining wears to adegree equal to the pitch of the thread 2 I, the rod l8 and tubularmember IT are extended to that degree. The use of the feeler memberensures that no adjustment of a brake block can be effected unlessitexceeds the path of movement of the feeler member, whatever may be thediameter of the brake drum, either normal or temporarily extended.

It will be understood that the facing l3 0 the feeler member should beof such a nature that it will not participate in the wear of the brakelinings 6, as in that case no result would be at tained. It shouldtherefore be extremely hard and resistant to wear in the conditionsprevailing, but'it will be noted that whereas the brake linings 6 aresubjected at every braking to the usual high frictional and wearingefiect, there is no positive pressure applied to the feeler member atany time to press it. upon the drum except the slight pressure necessaryto hold a tubular member ll against the pull of a rod l8 as extensionbetween these takes place.- At all braking periods between adjustmentmovements the contact of the facing I3 of the feeler member upon thebrake drum may be so finely adjusted that it is a mere touch.

In Figure 3 the assembly is substantially as shown in Figure l with theexception of the fact that the anchorage pin of one brake block isemployed as the means for mounting the connecting means between thefeeler and the other brake block; As before, there are a tubular bracket22 with the slidable metal member 23 having the head 24 and the hard anddurable lining 25, and upon each anchorage pin 4 is pivotally mounted abellcrank lever 25 which at 21 engages by one of its arms with therecess 28 in the member 23, the other arm of each bellcran'k lever beingarticulated at 29 to the adjusting member 39--3l articulated to a brakeblock.

t will be noted that in the forms above described one feeler member issuflicient for the purpose of adjusting two brake blocks, as each blockis provided with its adjusting member engaging with a feeler membercommon to both.

' Figure 4 illustrates another form of brake in which the anchorage pinsof the brake blocks 5 are utilised, these pins being however in thisform on opposite endsof a diameter and each brake block being forcedtowards the brake drum inbraking, by a separate hydraulic cylinder 32and piston 33. Upon each anchorage pin 4 is pivotally fitted in additionto the brake block, a bellcrank lever 34=35 of whichone arm 34 is facedwith the hard and durable lining 36, this arm constituting the feelermember. To the free end of theotherarrn of each bellcrank lever isarticulated one extremity of the adjusting member 31'38 of the formshown at l'll8 in Figure 1. Each lever arm terminates in a bifurcatedend 34a which embraces the end of a brake shoe 5, thus serving toposition the bellcrank lever 3435 in the released or brakes offposition, any adjustment of its brake block not affecting the length'ofthe path of movement of the feeler. The operation is as beforedescribed, only an excess of length of path of movement'of either brakevblock 'over' that of the feeler member causing adjustment.

In the .form' of adjustment shown in Figure 5 there is provided thebellcrank lever 39-40 with the facing 4| on one arm thereof, this armform ing the feeler, and each lever 394ll is provided upon an anchoragepin 4. To the outer end 39a of each arm 39 of a lever 39-40 isarticulated the rod 42 which atits other end is articulated to an arm 43pivoted upon brake shoe 5 by means of the pivot 'pin 44. As'shown inFigure 6 each such pivot pin 44 passes through the web of a brake shoe 5and bears a metal washer 45 into which the free end of such pin isriveted, a strong compression spring 46 being interposed between thewasher 45 and the brake shoe web. A further washer 41, formed of hardand durable frictional materialthe material employed for the feelerfacing is suitable--is mounted upon the pivot pin 44 as shown in thefigure.

In the operation of the brake according to Figure 5, assuming that theextent of movement of a brake shoe 5 to effect braking exceeds theextent of movement of the feelerarm 40 towards the brake drum 8, theobtuse angle formed by rod 42 and the arm. 43 increases, thus increasingthe effective length or distance between centres of pivot pin 44 and thearticulation 39a. The frictional washer 41 presents a strong resistanceto this movement but the said movement is effected by the strong brakingpressure and the arm 43 duly yields to the required extent, theadjustment of the brake being thus simply effected. On release of thebrakes the parts 39-40 and 42 return to their original positions asshown in Figure 5, but as the angle formed by arm 43 has been increasedit remains in that condition, there being no force to cause it to changeon the backward or release movement of the parts. The adjusted eifectivelength between pivot pin 44 and articulation 39a thus remains adjusteduntil a further adjustment of the brakes towards the brake drum 1 isrequired. This form of adjustment may be equally well applied in Figures1, 3, and 4 in substitution of the extensible adjustment members thereinshown.

Although any mechanical means may be employed for the mounting of abellcrank lever 39- 40 upon an anchorage pin, the means shown in detailin Figure 7 are found useful. The brake shoe 5 is mounted to pivot uponthe pin 4 cast on the backplate 3 and a screw 48 serves to secure thearm 39 of the bellcrank lever 39-40 which is connected to the arm 40 asshown. This provides a simple and eflective means of applying theadjustment means of this invention to an existing brake assembly, and aswill be understood may be equally well applied to the mounting of thebellcrank lever 26 of Figure 3 or the bellcrank lever 3435 of Figure 4.

Whilst I have shown and described the simplest and most accuratelyoperating methods known to me of carrying out the invention it will beunderstood that I do not confine myself to the precise details andarrangement of the parts, which may be varied within the scope of thedescription and of the following claims:

I claim:

1. In a brake assembly, a feeler member mounted upon the brake backplateand movable towards the brake drum, a brake block movable toward thebrake drum, an adjusting member adjustable as to effective length undertension and connected to the brake block, and means mounted upon thebrake backplate adapted to transmit the motion of the brake blockthrough the ad- .iustment member to the feeler member, until the lattermakes contact with the brake drum.

2. In a brake assembly, a feeler member mounted upon the brake backplateand movable towards the brake drum, a brake block movable toward thebrake drum, an adjusting member extensible in its effective length undertension connected at one end to the brake block, and a bellcrank leverpivoted upon a pin in the brake backpl'ate and having one arm. thereofconnected to the other end of the adjusting member, the other arm of thebellcrank lever engaging the feeler member and transmitting theretobodily motion of the brake block and adjusting memher.

3. In a brake assembly having two brake blocks,

era-v a feeler member mounted upon the brake backplate and slidablymovable towards the brake drum, an adjusting member adjustable as toeffective length under tension and connected to one brake block, and abellcrank lever pivoting upon a pivot point constituted by an anchoragepin of the brake block other than that to which the adjusting member isconnected, the said adjusting member and the feeler member beingconnected by the bellcrank lever.

4. In a brake assembly having two brake blocks pivoted upon anchoragepins at opposite points upon the brake backplate, with means forimpelling each brake block separately towards the brake drum, two feelermembers mounted upon the backplate and each movable towards the brakedrum, an adjusting member connected to each brakeblock, and meansmounted upon the backplate adapted to transmit braking motion of eachbrake block through its adjusting member to its feeler member.

5. In a brake assembly having two brake blocks pivoted upon anchoragepins at opposed points upon the brake backplate, with means forimpelling each brake block towards the brake drum, two feeler membersmounted upon the backplate and each movable towards the brake drum in alength of path equivalent to the normal length of path of a brake blockin braking, an adjusting member adjustable as to effective length undertension connected to each brake block, and means mounted upon thebackplate adapted to transmit braking motion of each brake block throughthe adjusting member to its feeler member.

6. In a brake assembly having two brake blocks pivoting upon anchoragepins at opposed points upon the brake backplate, with means forimpelling each brake block towards the brake drum, two feeler memberseach movable towards the brake drum, a bellcrank'lever pivoted upon ananchorage pin of each brake block, one arm of each bellcrank leverbearing a hard brake lining and constituting the feeler member, and anadjusting member connected to each brake block and to an arm of thebellcrank lever pivoted upon the anchorage pin of the other brake block.

'7. In a brake assembly having two brake blocks pivoting upon anchoragepins at opposed points upon the brake backplate, with means forimpelling each brake block towards the brake drum, two feeler memberseach movable towards the brake drum, a bellcrank lever pivoted upon ananchorage pin of each brake block, one arm of each bellcrank leverbearing a hard brake lining and constituting the feeler member, and anadjusting member, adjustable as to effective length under tension,connected to each brake block and to an arm of the bellcrank leverpivoted upon the anchorage pin of the other brake block.

8. In a brake assembly a pair of brake blocks, a feeler member mountedupon the b-ackplate of the brake and slidably movable towards the brakedrum, an adjusting member connected to each brake block, bellcranklevers pivoting upon the brake backplate, one arm of each lever beingconnected to said adjusting member, and engaging means upon the feelermember which means are engaged by and receive motion from the other armsof the bellcrank levers.

9. In a brake assembly, a feeler member mounted upon the brake backplateand movable towards the brake drum, a brake block movable toward thebrake drum, a two-part articulated adjusting member connected at one endto the brake block, friction means between such end and such brakeblock, and a bel'lcrank lever pivoted upon a pin in the brake backplate,the other end of the two-part adjusting member being connected to an armof said bellcrank lever, the other arm of the bellcrank lever carryingthe feeler member.

10. In a brake assembly having two brake blocks pivoting upon anchoragepins at opposed points upon the brake backplate, with means forimpelling each brake block towards the brake drum, two feeler memberseach movable towards the brake drum, a bellcrank lever pivoted upon ananchorage pin of each brake block, one arm of each bellcrank leverbearing a hard brake lining and constituting the feeler member, and anadjusting member consisting of a longitudinally extensible two-partmember connected to each brake block and to an arm of the beilcranklever pivoted upon the anchorage pin of the other brake block.

11. In a brake assembly having tWo brake blocks pivoting upon anchoragepins at opposed points upon the brake backplate, with means forimpell-ing each brake block towards the brake drum, two feeler memberseach movable towards the brake drum in a length of path equivalent tothe normal length of path of a brake block in braking, a bellcrank leverpivoted upon an anchorage pin of each brake block, one arm of eachbellcrank lever bearing a hard brake lining and constituting the feelermember, and an adjusting member consisting of an articulated two-partmember connected to each brake block and toan arm of the bellcrank leverpivoted upon the anchorage pin of the other brake block, and frictionmeans between each brake block and its connected end of the two-partmember.

12. In a brake assembly having two brake blocks and a further memberserving as a feeler member, all having equivalent lengths of path ofmovement towards the brake drum when the brake blocks are unworn, meansfor imparting the movement of each brake block separately to the feelermember, such means being changeable as to form on excess movement ofeither brake block occurring as a result of its wear over the length ofmovement of the feeler member, for the purpose set forth.

13. In a brake assembly the combination with a brake drum, a brake blockmounted for braking movement toward the brake drum and retractilemovement from the brake drum, an adjustable device for limiting theretractile movement of the brake block, means normally actuated by thebrake block during its braking movement cooperating with the adjustabledevice to reset the adjustable device to compensate for wear of thebrake block, and means sensitive to expansion or wear of the brake drumcooperating with the first mentioned means to control the resetting.

14. In a brake assembly, the combination with a brake drum, a backplate, and a brake block mounted on the back plate and movable towardand from the drum, of a feeler member carried by the back plate andmovable toward and from the drum, and an adjustable connection betweenthe brake block and feeler member arranged to limit the retractilemovement of the brake block from the drum and actuated upon movement ofthe brake block toward the drum to move the feeler member toward thedrum, the adjustable connection being so constructed and arranged thatmovement of the brake block toward the brake drum tends to reset theconnection when,

but only when, the movement of the brake block toward th brake drum isrelatively greater than the movement of the feeler member toward thebrake drum.

15. In a. brake assembly the combination with a brake drum, a backplate, a brake block mounted on the back plate for braking movementtoward and retractile movement from the brake drum, of a feeler membermounted on the back plate movable toward and from the brake drum, anadjustable device for limiting the retractile movement of the brakeblock, and means actuated upon movement of the brake block and feelermember toward the brake drum to reset the adjustable device when themovement of the brake block, due to wear of the brake block, isexcessive as compared with the simultaneous movement of the feelermember. i

16. In a brake assembly the combination with a brake drum, a brake blockmounted for braking movement toward the brake drum and retractilemovement from the brake drum, of an adjustable device for limiting theretractile movement of the brake block, a feeler member mount ed forforward movement toward the brake drum, means for transmitting brakingmotion of the brake block to the adjustable device and tending to causeresetting thereof and means for transmitting movement of the adjustablemember to the feeler member to move the feeler member forward againstthe brake drum, said last mentioned means cooperating with the firstmentioned means to tend to caus resetting of the adjustable device asthe feeler member engages the brake drum.

17. In a brake assembly the combination with a brake drum, a brak blockmounted for braking movement toward the brake drum and retractilemovement from the brake drum, of an adjustable device for limiting theretractile movement of the brake block, and means for resetting theadjustable device upon wear of the brake block comprising a feelermember movable toward and from the brake drum and connections operatedby th brake block and feeler member to reset said adjustable device.

18. In a brake assembly having two brake blocksand a further memberserving as a feeler member, all movable toward and from the brake drum,means adapted to be actuated by movement of either brake block towardthe brake drum to move the feeler member toward the brake drum, suchmeans being changeable as to form on movement of either brake blockwhenever such movement, due to wear of the brake block, is excessive ascompared with the simultaneous movement of the feeler member.

19. In a brake assembly, the combination. with a brak drum and a brakeblock mounted for braking movement toward the brake drum and retractilemovement from the brake drum of adjustable means for limiting theretractile movement of the brake block comprising a lever, a feelermember connected to one arm thereof for movement toward and from thebrake drum, an adjustable link connecting the other arm of the lever andthe brake block and adapted to bereset by movement of the brake blocktoward the brake drum in excess of the movement necessary to press thefeeler member against the drum.

20. In a brake assembly having two brake blocks and a member serving asa feeler member, each normally having a movement of predetermined lengthof path toward the brake drum when the brake blocks are unworn, meansfor imparting movement of either brake block to the feeler member, suchmeans being changeable as to form on movement of either brake blockwhich due to wear exceeds relatively the simultaneous movement of thefeeler member.

21. In a brake assembly the combination with a brake drum, a brake blockmounted for braking movement toward the brake drum and retractilemovement from the brake drum. of an adjustable device for limiting theretractile movement of the brake block, and means cooperating with theadjustable device to reset the same by applying stress thereto during abrake applying movement comprising a feeler member movable toward andfrom the brake drum and stress transmitting connections between thefeeler membe: and a part of the adjustable device.

ERNST 'I'RACHSEL.

